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WASHINGTON (WUSA9) -- Animal keepers at the National Zoo have been hand feeding the first born pup at the zoo in 23 years, a female gray seal pup that was born in January.

Zoo keepers said they have been monitoring the pup and her mother closely throughout the past few months. Within 48 hours of the pups birth, the animal care team began preparations to hand feed the pup as she was not gaining weight while nursing from her mother, zoo officials said.

"Our animal care team is always prepared to hand rear or hand feed an animal if they need to," said Ed Bronikowski, senior curator at the Zoo. "In the first days of this pup's life we did not see her gain as much weight as we would have expected. It is still a tenuous time, but the pup's weight is now heading in the right direction. We celebrate every pound that she gains."

Veterinarians and nutritionists came together and made a plan to supplement the pup's nutritional needs, officials said. Zoo keepers have been tube feeding the pup and she now weighs 44 pounds, which is up by 10 pounds from her birth weight.

Zoo officials said in the wild, gray seals usually nurse from their mothers for about 15 to 21 days and gain a lot of weight during that time. The mortality rate for gray seal pups that have not been in the wild varies between 5 and 20 percent; it can sometimes be as high as 30 percent.

The pup will be joining the zoo's four adult gray seals and two harbor seals on exhibit in the spring, zoo officials said.